The invention relates to a semiconductor chip assembly system with a suction nipple for removing a semiconductor chip from a carrier film and for positioning and setting down the semiconductor chip in a component position of a lead frame for electronic components.
With increasing miniaturization of semiconductor chips, in particular with increasing reduction of the volume of the semiconductor chips by reducing the thickness of the semiconductor chips by etching or grinding them thin, to a thickness of only a few tenths of micrometers, the handling of semiconductor chips in a semiconductor chip assembly system is becoming increasingly more difficult. At present, the failure rate when using standard handling tools in a semiconductor chip assembly system is already approximately 20%. With such a high proportion of damaged miniaturized semiconductor chips, in particular in the case of semiconductor chips intended for radio-frequency applications, it is necessary to reduce the failure rate. Particularly high failure rates occur in semiconductor chip assembly systems that are used for xe2x80x9cdie bondingxe2x80x9d. In this case, the semiconductor chip is removed from a carrier film that is adhesive on one side and brought into a position in which the semiconductor chip is fixed on a chip island of a lead frame in a component position for producing an electronic component.
It is accordingly an object of the invention to provide a semiconductor chip assembly system with a suction nipple for removing a semiconductor chip that overcomes the above-mentioned disadvantages of the prior art devices of this general type, with which the failure rate in the handling and transporting of the semiconductor chip within the semiconductor chip assembly system is reduced.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor chip assembly system. The system contains a suction nipple for removing a semiconductor chip from a carrier film and for positioning and setting down the semiconductor chip in a component position of a lead frame for electronic components. The suction nipple includes a dimensionally stable cylindrical mouthpiece with a suction bore formed therein, a rubber-elastic region adjoining the cylindrical mouthpiece, and a dimensionally stable suction tube attachment extending from the rubber-elastic region.
According to the invention, a semiconductor chip assembly system is provided, which system is equipped with a suction nipple for picking up a semiconductor chip from a carrier film and at the same time holds the semiconductor chip for positioning it and setting it down in a component position of a lead frame for electronic components. For this purpose, the suction nipple has a dimensionally stable cylindrical mouthpiece with a suction bore, which is adjoined by a rubber-elastic region of the suction nipple which goes over into a dimensionally stable suction tube attachment.
When a suction nipple is used in a semiconductor chip assembly system, it is under vacuum as soon as a surface of the semiconductor chip closes its suction opening. The dimensionally stable configuration of a cylindrical mouthpiece has the effect of ensuring that the mouthpiece does not collapse, deform or in some other way damage or lose the semiconductor chip during the manipulation within the semiconductor chip assembly system. What is more, the dimensionally stable cylindrical mouthpiece has the effect of ensuring that the surface of the semiconductor chip can support itself on a dimensionally stable surface of the cylindrical mouthpiece.
The rubber-elastic region of the suction nipple adjoining the mouthpiece allows the nipple to adapt itself to the position of the upper side of the semiconductor chip without exerting damaging pressure on the semiconductor chip. Rather, the mouthpiece is rubber-elastically cushioned and can consequently be set down gently on the surface of the semiconductor chip. The adjoining dimensionally stable suction tube attachment of the suction nipple ensures that the suction tube attachment of the suction nipple can be connected in a gastight manner to a corresponding vacuum tube or a vacuum line. In this case, the dimensionally stable suction tube attachment supplies the rubber-elastic region and the dimensionally stable cylindrical mouthpiece of the suction nipple with a vacuum during operation, without itself collapsing and consequently putting at risk the secure holding of the semiconductor chip.
The inside diameter of the suction tube attachment is many times greater than the suction bore of the cylindrical mouthpiece. The rubber-elastic region consequently forms the transition from the suction bore to the many times greater diameter of the suction tube attachment. For this purpose, the rubber-elastic region has an inner cone and an outer cone, which between them has a thin rubber-elastic wall. The configuration of the inner cone and outer cone allows the elasticity of the rubber-elastic region to be varied and set to the requirements of the semiconductor chip assembly system for miniaturized semiconductor chips. The choice of the same slope of the inner cone and outer cone allows a constant wall thickness of a rubber-elastic material from the suction tube attachment to the mouthpiece to be realized. The wall thickness itself may in this case be made to match very precisely the loading capability of the semiconductor chips to be held.
To achieve decreasing elasticity of the rubber-elastic region with increasing deformation of the rubber-elastic region, this region may have between the inner cone and the outer cone a wall thickness of a rubber-elastic material that becomes thinner toward the mouthpiece. If there is slight deflection of the cylindrical mouthpiece in the axial direction, consequently a high rubber-elasticity is initially provided, decreasing as the degree of deformation of the rubber-elastic region increases. With such a configuration of the suction nipple, the deformation resistance becomes greater as the deformation of the rubber-elastic region of the suction nipple increases.
The size of the rubber-elastic region is substantially determined by the area ratio between the cross section of the suction bore of the mouthpiece and the inner cross section of the suction tube attachment. To achieve effective cushioning by the rubber-elastic region of the cylindrical mouthpiece, this area ratio lies between 1:9 and 1:16.
Apart from the area ratio, the length of the rubber-elastic region in the axial direction is decisive for the elasticity of the region. The greater the length, the more rigid the rubber-elastic region becomes in the axial direction. A preferred ratio between the length of the rubber-elastic region in the axial direction in relation to the inside diameter of the suction tube attachment lies between 1:2 and 1:4. The smaller the ratio becomes, the softer and more elastic the rubber-elastic region will act. However, if the ratio goes below 1:4, the risk increases of the vacuum within the suction tube attachment alone causing the dimensionally stable mouthpiece to be inverted into the interior space of the suction tube attachment and the suction nipple consequently no longer being serviceable.
The ratio of the length of the rubber-elastic region in the axial direction to the diameter of the suction bore of the mouthpiece should also not exceed a range from 1:1 to 3:1. Here, too, outside this range there is, on the one hand, a risk of the rubber-elastic region becoming rigid and, in the opposite direction, the risk of the mouthpiece being inverted into the interior space of the suction tube attachment.
To ensure the dimensional stability of the cylindrical mouthpiece and of the suction tube attachment in comparison with the rubber-elastic region, the wall thickness of the rubber-elastic region may be less than or equal to the wall thickness of the cylindrical mouthpiece and, in any event, less than the wall thickness of the suction tube attachment. If these conditions are maintained, it can be assumed that the requirements to be met by the individual regions of the suction nipple when picking up a semiconductor chip are satisfied.
Diameters between 100 and 500 xcexcm have proven to be optimal for the suction tube bore and sizes between 250 and 1200 micrometers have proven to be optimal as the outside diameter of the cylindrical mouthpiece. In contrast, the inside diameter of the suction tube attachment should lie between 800 and 1200 micrometers.
The transition from the suction tube attachment of the suction nipple to a vacuum tube or a vacuum line in the semiconductor chip assembly system can be ensured by an outer plug cone of the suction tube attachment, with which the suction nipple can be fitted in a vacuumtight manner into a suction tube or a vacuum line. This has the advantage of quick and easy exchangeability of the suction nipple, which has a limited service life on account of its sensitive mouthpiece and the no less sensitive rubber-elastic region.
To place the mouthpiece onto the surface of a semiconductor chip in a plane-parallel manner, the mouthpiece has a disk-shaped suction mouth. The disk-shaped suction mouth is highly polished and planar, to establish a connection that is as vacuumtight as possible between the surface of the semiconductor chip and the disk-shaped suction mouth. It is even possible to compensate for inclinations of the surface of the semiconductor chip, because according to the invention the dimensionally stable mouthpiece is adjoined by a rubber-elastic region that compensates for angles of inclination of the surface of the semiconductor chip with respect to the surface of the disk-shaped suction mouth.
For this compensation and for the operation of lifting a semiconductor chip off a carrier film that is adhesive on one side, it is provided that the rubber-elastic excursion in the axial direction of the mouthpiece on account of the rubber-elastic region of the suction nipple can be up to 1000 xcexcm. Such a great rubber-elastic excursion in comparison with the thickness of the chip ensures that the dimensionally stable mouthpiece with its suction opening does not cause any damage when it is placed onto the surface of the semiconductor chip. Furthermore, the rubber-elastic excursion ensures that the raising of the semiconductor chip by a lifting needle from the rear side of the semiconductor chip does not lead to the upper side of the semiconductor chip becoming damaged by the dimensionally stable mouthpiece of the suction nipple. In such a semiconductor chip assembly system, the lifting needle itself is an auxiliary tool with which, on the one hand, the film on the rear side of the semiconductor chip is pierced and, on the other hand, the semiconductor chip is centrally raised and detached from the layer of adhesive of the film and lifted against the dimensionally stable mouthpiece of the suction nipple. The suction nipple according to the invention consequently ensures a rubber-elastic excursion that cushions the raising by the lifting needle from the rear side of the semiconductor chip on the upper side of the semiconductor chip and consequently reduces damage to the semiconductor chip.
The suction nipple may be produced in one piece with its suction tube attachment, its rubber-elastic region and its mouthpiece from a plastic injection-molding compound. In the case of such a one-piece embodiment, the dimensional stability of the mouthpiece and the dimensional stability of the suction tube attachment are ensured by corresponding wall thicknesses both of the mouthpiece and of the suction tube attachment. Although, as a result, the regions of the suction nipple with thick walls likewise have rubber-elastic properties, considerably higher forces would be required for deforming these regions than for the region of the suction nipple that, by appropriately thin walls in comparison with the dimensionally stable region, has correspondingly higher elasticity.
Such a suction nipple may be produced from an elastomeric plastic. Elastomeric plastics have the advantage that they recover their basic shape even under extreme deformation. Consequently, the rubber-elastic region itself will go back into its original position even in the case of the extreme rubber-elastic excursion of 1000 xcexcm, if the entire suction nipple is produced from an elastomeric plastic.
As a one-piece component, the suction nipple may contain a thermoplastic rubber of a mixture of polypropylene and olefins. Such a mixture has the advantage over other types of rubber that it is particularly tear-resistant and has high impact strength. This increases the service life and serviceability of the suction nipple in comparison with suction nipples made of other elastomers.
To sum up, it can be stated that the special configuration of the xe2x80x9cdie-bonding toolxe2x80x9d allows mechanical and electrical damage to the semiconductor chip to be avoided. In addition, it has been found that the embodiment of the suction nipple proposed in this invention can be produced at lower cost by a factor of 100 than known variants. The special configuration of the suction nipple or of the xe2x80x9cdie-bonding toolxe2x80x9d together with the aforementioned material selection allows damping properties and elastic properties of the material to be deliberately used to ensure gentle handling of the semiconductor chips in the semiconductor chip assembly system according to the invention.
During the xe2x80x9cpickupxe2x80x9d, that is the lifting of the semiconductor chip off a wafer sawn into semiconductor chips on a carrier film that is adhesive on one side, the xe2x80x9ctoolxe2x80x9d moves with the suction nipple onto the surface of the chip. As this takes place, a specifically intended deformation of the lower part of the tool occurs, and is used for damping, or the damped placement, of the tool onto the surface of the chip. After removal of a chip by the tool, the deformation reverts to the original shape again. The material selection in the form of a thermoplastic rubber results in that the service life of the tool is not adversely affected. Even semiconductor chips that are weakened by xe2x80x9cvia holesxe2x80x9d can be assembled unimpaired and undamaged in the semiconductor chip assembly system. Even chips which have been etched thin and the thickness of which is below 100 xcexcm can be processed unimpaired with this semiconductor chip assembly system. It has been possible to demonstrate that, by using the semiconductor chip assembly system with a suction nipple which has a rubber-elastic region, the failure rate in xe2x80x9cdie bondingxe2x80x9d can be reduced to a few individual chips, with the result that the yield can be increased by almost 20%.
In accordance with a concomitant feature of the invention, a lifting needle is disposed opposite the cylindrical mouthpiece for removing the semiconductor chips from a carrier film. The lifting needle has a lifting range which ensures piercing of the carrier film and the lifting of the semiconductor chip off the carrier film and the holding of the semiconductor chip against the cylindrical mouthpiece of the suction nipple.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor chip assembly system with a suction nipple for removing a semiconductor chip, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.